Crystal controlled oscillator



July 9, 1935. F. BYRNES V CRYSTAL CONTROLLED OSCILLATOR mama? FiledMarch 30, 1953 2 Sheets-Sheet 1 0 E 1. .7 w M\ 38 l l l l INVENTORIRVING FRANCIS BYRNES BY 9% J ATTORNEY July 9, 1935. BYRNES 2,007,637

CRYSTAL CONTROLLED 050 I LLATOR Filed March 30, 1933 2 Sheets-Sheet 2/2) l I k 6 40 R54 ///4 78 6 g 24 104 I 00 4 g 7g 210 z E 2% "umo 1 1 ifma 706? 1/2 1/8 INVENTOR IRVING FRANCIS BYRNES ATTORNEY Patented July 9,1935 UNITED STATES:

CRYSTAL CONTROLLED oscILLA'roR Irving Francis Byrnes, Riverdale, N. Y.,assignor to Radio Corporation of America, a. corporation of DelawareApplication March30,19 3 3, Serial No. 663,435

7 '7 Claims. (01. 25036) controlled oscillation generators adapted foruse in transmitters, receivers and frequency meas uring systems, and hasparticular reference to constant frequency oscillation generators for ause in aircraft.

Things much to be desired in, for example, oscillation generators foraircraft transmitters are, operation at a constant predeterminedfrequency, simplicity of construction, simplicity of adjustment, absenceof critical settingsand freedom from undesired parasitic oscillations.Moreover, when crystal controlled oscillation generators are used, it ishighly desirable to obtain a reasonably high power output in order toeliminate the weight and cost of subsequent amplifiers. When obtaining ahigh power output from a crystal controlled oscillator it is alsodesirable to prevent undue stress of the crystal, or, in other words, toobtain a high power output without having a large current flow throughthe crystal. I

To provide for these prime desiderata is, there'- fore, theprincipalobject of my present invention. In carrying it into effect Iconnect the serial combination of a-high. reactance and a piezo-electriccrystal between a control or cold electrode and cathode of an electrondischarge device whereby the high reactance prevents energization of thecrystal which would otherwise occur due to the interelectrode capacityof the elements of the device or tube. In the alternative or inaddition, I provide electrodes within the tube to eliminate, or assistin eliminating the undesired interelectrode feed back. For desired feedback purposes I couple the anode orv plate circuit to the controlelectrode or active side of the frequency controlling piezo-electriccrystal, by means of a variable resistor whereby desired operationensues, namely, excitation of the crystal in such a way as to give areasonably high power output witha reasonable minimum of current flowingthrough the crystal.

Further understanding of my present inven tion may best be obtained byreferring to the accompanying drawings although, of course, as requiredby law, it is defined with particularity in the appended claims.

Figure l of the drawings ilustrates in wiring diagram form a preferredmodification of my present invention wherein undesiredinter-eleccapacitorgfjor reducing interelectrode feed back is aided bythe use of electrodes intermediate the control electrode and anode ofthe tube forming part of my oscillation generator;

Figure 3 illustrates, according to my present invention, a pushpull formof oscillation generator; and,

Figure 4 is a'wiring diagram of my present invention wherein the screengrid of a tube is used as the anode or plate.

A Referring in greater detail to the drawings and in particular toFigure 1, I have illustrated dia-- grammatically an electron dischargedevice having within an hermetically sealed container 2, a cathode 4, acold control electrode or grid ii and an anode 8. The cathode 4 may, ofcourse, be of then. C. energized type, or of the filamentary D. C.energized type as illustrated; it may be of the indirectly heated type,or it may be what is known as a cold cathode. The control elec-v trodeor grid 6 is spaced from the anode i and is subjected to aunidirectional negative potential by the action of a grid leak resistorl0, which may be replaced by the serial combination of a choke coil anda source of negative biasing potential.

Between the control electrode 6 and cathode 4 there is connected a highimpedance in the form of a small condenser [2 in series with the twoelectrode piezo-electric crystal M. The condenser 12, because of itssmall size, has a high capacitive reactance at the operating frequencyof the-crystal, and prevents energization of the piezo-electric crystalI4 which would otherwise occur due to the interelement capacity existingbetween the anode 8 and the control electrode 6.

Between the anode 8 and the cathode 4 there is connecteda circuit l6having inductance and capacity. Theinductance is provided by the coill8, connected intermediate its ends, through conductor 20 and by-passingcondenser 22, to the cathode 4. The capacity of the circuit may be dueto the distributed capacity of the-coil i8 alone orin combination withthe capacity existing between the anode and cathode. This capacity maybe augmented, if desired, by the addition of a variable tuning condenser24.

.In order to establish a desired feed back, I have shown in Figure 1 acircuit having a variable resistor 26 connected between the anode oranode circuit andthe control electrode 6 and through the controlelectrode side or terminal of condenser i2 to the active electrode ofthe piezo-electric crystal l4. To prevent the application ofunidirectional plate potential or anode potential on to the grid 6 ofthe tube, there is inserted in this coupling circuit comprisingconductors 28, 36, a blocking condenser 32. Also, it will be noted thatthe coupling circuit or resistor 26 is connected to the lower end ofcoil I8 and hence the volt-' ages fed back tothe control electrode arein sub.-

stantial opposite phase relation to those existing upon the anode which,as apparent to those skilled in the art, is the correct condition foroscillation generation. This action will occur with a circuit asdescribed at only a frequency corresponding to one of the natural modesof vibration of the piezo-electric crystal l4. 7

In the foregoing circuit no oscillations will be produced with thecrystal removed and similarly, with the coupling resistor 26 removed, nooscillations will be produced. By removed I mean actual removal andconsequent opening of the circuit 28 and 38, to show that there is notenough feed back through 12 to sustain oscillation. With resistor 26shorted there will be excessive feed back and crystal may then notdetermine frequency of oscillations.

Output energy may be taken from the conductors 34 and fed directly to aradiating antenna (not shown). The energy fed into the antenna may bemodulated by impressing, through the medium of an audio frequencytransformer 36, audio frequency voltages upon the anode potential supply38.

I have found that the circuit described in Figure 1 is easy to constructand requires no critical settings, and these features are highlydesirable in apparatus for use in, for example, aircraft transmitters.As already pointed out, removal of the coupling resistor or the crystalstops oscillations. The crystal, therefore, is in full control of theoscillation frequency and this 'may readily be proved by changing thetuning of the output circuit I6 either by varying its inductance or byvarying the tuning condenser 24; or, by changing the plate or filamentvoltage. Moreover, I have found that the current through the crystal isonehalf to one-quarter of that which flows in other circuits, which I amaware of, for a given output from the tube.

In the arrangement shown in Figure 2, action of the small condenser orthe highly capacitive reactor [2 in preventing excitation of the crystal1 4 due to interelectrode capacity of the tube 2 is aided by theaddition of a screen grid 40 and/or a suppressor grid 42, the former ofwhich is grounded for radio frequency currents by means of a by-passingcondenser 44 and maintained at a suitable unidirectional positivepotential by the action of voltage dropping resistor 46. It is to beclearly understood, however, that condenser I 2 may be entirely omittedif the suppressor 42 and/or screen grid 40 act to prevent feed backother than the desired feed back through resistor 26. The suppressorgrid is grounded by the action of a by-passing condenser 48 andmaintained at a suitable negative potential by means of conductor 50tapped to potential biasing source 52 which may be used directly, ifdesired, in conjunction with resistor I0, to subject control electrodeor grid 6 to a suitable negative potential. Also, in the arrangementshown in Figure 2, feed back may be accomplished by use of a couplingcoil 54 grounded as shown and inductively coupled to inductance coil l8,although, if desired, electrostatically shielded therefrom through themedium of a grounded shield 56. In the event that coils I8 and 54 aremounted concentrically, shield 56 may be made concentric therewith andpreferably in the form of a slitted, grounded metallic cylinder mountedbetween the coils.

By impressing voice currents upon transformer 58, modulator tube 60 willcause varying currents to flow through inductive reactor 62, which, ifdesired may be a resistor, and hence the out.-

put of the system shown in Figure 2 will be modulated in accordance withthe signal or voice currents impressed upon transformer 58. Themodulated output of oscillator 2 may then be fed into a power amplifier64 and radiated by a suitable antenna 66.

In the event of operation at exceedingly high frequencies, theinductance of the leads to the screen and suppressor grids may beinsufficient to prevent their maintenance at ground potential. In thatcase condensers 44, 48 may be reduced in value so as to series resonatewith the leads thereby maintaining the suppressor and screen grids atground potential.

My present invention is not limited to single tube oscillators; for, asshown in Figure 3 my invention may be applied to a pushpull arrangementof, for example, screen grid tubes 2, 10. The crystal M in this case isblocked off from the control grids 6, 12 by small condensers l2,

'14 having relatively high capacity reactance.

These condensers prevent oscillation generation due to interelectrodefeed back and this form of feed back may be reduced to a still lesservalue by means of screen grids 40, 18, grounded by by-passing condenser44 and maintained at a suitable operating potential by means of tap 18connected to the anode source 80. The plates 8, 82 of the tubes areconnected in phase opposition by means of an inductance coil 94 whichmay be so chosen as to have a suitable resonant period with its owndistributed capacity. Or, if desired, a tuning condenser may be variablyconnected across the entire coil or any portion thereof. This statement,of course, applies equally well to the other arrangements such as shownin Figure 1, wherein, for example, condenser 24 may not only beconnected in the position. shown, but may be connected across the lowerhalf of coil l8 or across a lower and upper portion of coil [8, or ifdesired, across the complete coil.

Turning back to Figure 3, desired feed back may be accomplished by theuse of solely variable resistor 26 and blocking condenser 32 connectedbetween grid 6 and a point on coil 94 below the intermediate platetapping point 88. Preferably, however, I provide a symmetricalarrangement of feed back circuits and as shown, to do so, a variableresistor 90 and blocking condenser 92 forming a circuit connectedbetween a point 84 on coil 94 above tapping point 88 and to grid 12 oftube 10, are provided. The grids are subjected to a suitable operatingpotential by the action of grid leak resistors Ill, 96.

Output energy may be fed to a modulator 98 and then to a power amplifierand/or frequency multipliers I whose output may then be fed into ratiofrequency transmission lines or preferably into a radiating antenna I82.If desired, the frequency multipliers may be placed ahead of themodulator.

In Figure 4 I have shown an arrangement wherein the various features ofmy present invention may be utilized in an oscillation generator whereinthe screen grid 40 is used as a plate. Since the connections are similarto the arrangement shown in Figure 1, no detailed remarks concerningthis circuit need be given. However, it may be pointed out that theanode 8 is coupled to the oscillatory system formed of the con trol grid6, screen grid 40, cathode 4, the crystal, and the other necessaryelements of the oscillatory circuit, only by way of the electron streamwithin the tube 2. The anode or output circuit of tube 2 may be in theform of a tunable circuit IM which may be tuned to some harmonic of thecrystal M if desired. Moreover, harmonic production in the tunablecircuit I04 may be facilitated by varying the relative poten-- tials onthe plate 8 and screen grid lil bysuitable adjustment of taps I66, H38respectively on source Hi3. Output energy from the output circuit I04may be fed to a first detector l E2 to which is also fed, from amplifierH 5, radiant energy collected upon antenna H6. The output of the firstdetector H2 may then be fed after suitable amplification, if desired, toa second detector Hi5 whose output after audio frequency amplificationmay be fed to a translating device such as ear phones are.

Also, in the arrangement shown in Figure 4, output energy may be takenand utilized in any desired way from the screen grid tunable circuitformed of coil l8 and tunable circuit E i which, of course, may beplaced across any portion of the coil it. Thus, for example, the outputof coil [8 and tunable circuit 24 may be inductively fed into suitablecircuits to control the frequency of oscillation of a transmitterwhereas simultaneously output energy from circuit we may be used tocontrol as shown a receiving circuit or vice versa. In addition, circuitltd may obviously be replaced by a simple coil or by a resistor fromwhich output energy may be taken in ways well known to the art.

In the claims which follow the term anode is to be taken as not onlyincluding an anode such as plate 8 of Figure 1, but also is to be givena broader construction so as to include a. tube element such as screengrid ill of Figure 4.

Having thus described my invention, what I claim is:

1. A constant frequency oscillation generator comprising an electrondischarge device having Within an hermetically sealed container ananode, a cathode, and a control electrode; a piezoelectric crystalconnected between said control electrode and cathode; a reactor inseries with said crystal and connected between said crystal and saidcontrol electrode for preventing eX- citation of said crystal due tointerelectrode feed back; a circuit interconnecting said anode andcathode; and, another circuit coupling said anode circuit to the controlelectrode side of said reactor for causing energization of said crystaland hence oscillation generation at a frequency fixed by said crystal.

2. An oscillation generator comprising an electron discharge devicehaving within an hermetically sealed container an anode, a cathode, anda control electrode; the series combination of a small condenser and apiezo-electric crystal connected between said, control electrode andcathode, one side of said small condenser being connected to saidcontrol electrode and the other side of said condenser being connectedto said crystal, said small condenser acting to prevent excitation ofsaid crystal by virtue of the interelectrode capacity of said device;and, a coupling circuit between the anode of said device and the controlelectrode side of said small condenser for causing desired energizationof said crystal and hence the production of oscillations of said deviceat a frequency fixed by said crystal.

3. An oscillation generator comprising an electron discharge devicehaving within an hermetically sealedcontainer an anode, a cathode, and

a control electrode, the serial combination of a small condenser and apiezo-electric crystal connected between said control electrode andcathode, one terminal of said small condenser being connected to saidcontrol electrode and the other to said crystal, a circuitinterconnecting said anode and cathode; and, a circuit including avariable resistor for establishing feed back from said anode to thecontrol electrode side of said small condenser whereby oscillations areset up at a frequency determined by said crystal.

4. An oscillation generator comprising a two electrode. piezo-electriccrystal, an electron discharge device having Within an hermeticallysealed container an anode, a cathode and a control electrode, the serialcombination of a small condenser which is highly reactive at theoperating frequency of the crystal and said two electrode piezo-electriccrystal, connected between said control electrode and cathode, saidsmall condenser having one side connected to the corn trol electrode andthe other side to said crystal; a circuit having inductance and capacityconnected between said anode and cathode, and,'a variable resistorcoupled to the control electrode side of said small condenser and anodefor establishing desired feed back whereby oscillations of a frequencydetermined by said crystal occur in said circuit having inductance andcapacity.

5. An oscillation generator comprising a two electrode piezo-electriccrystal, a vacuum tube having an anode a cathode and a controlelectrode, the series combination of a small condenser which is highlyreactive at the operating frequency of the crystal and said twoelectrode piezo-electric crystal connected between said controlelectrode .and cathode said small condenser having one terminalconnected to said control electrode and its other terminal to saidcrystal; a grid leak resistance connected between said control electrodeand cathode, and, the series combination of a blocking condenser and avariable resistor connected between said anode and the control electrodeside of said small condenser whereby feed back for causing oscillationgeneration at a frequency determined by said crystal, is established.

6. Apparatus as claimed in claim 5 wherein, for assisting said smallcondenser which is highly reactive at the operating frequency of thecrystal for preventing excitation of said crystal due to interelectrodefeed back, there is provided in addition an electrode between saidcontrol electrode and cathode, and means for maintaining said additionalelectrode at a suitable unidirectional potential.

7. A constant frequency oscillation generator comprising an electrondischarge device having within an hermetically sealed container ananode, a cathode, and a control electrode; a piezo-electric crystalconnected between said control electrode and cathode; a reactor inseries with said crystal for preventing excitation of said crystal dueto interelectrocle feed back said reactor being connected between saidcontrol electrode and said crystal; a circuit interconnecting said anodeand cathode; and, another circuit including a resistor coupling saidanode circuit to the grid side of said reactor for causing energizationof said crystal and hence oscillation generation at a frequency fixed bysaid crystal.'

IRVING F. BYRNES.

